1. Field of the Invention
The present invention relates to image combining method for combining background image, handwritten image, and standard image.
2. Description of the Related Art
Recently, a wide-spread use and high performance of digital cameras, scanners, and printers has led to various usages of photo images other than simply printing the digital photo image on a recording sheet.
For example, there are techniques of adding handwritten characters and pictures on the photo image and combining standard digital image data such as an illustration to the photo image. A user can use such techniques to create a postcard by writing a message on the photo image captured by the digital camera and combining the photo image with a decoration frame.
There are several methods for combining handwritten characters and pictures or a standard image with the photo image input from an image input device such as the digital camera or the scanner.
U.S. Patent Application Publication No. US 2005/0213174 discusses printing a document sheet in which an input photo image is combined with the standard image. The user then writes characters and pictures in a handwritten region of the printed document sheet. The document sheet is read, and the handwritten image is superposed on and combined with the photo image. Further, the photo image is printed in the handwritten region of the document sheet, so that the user can recognize the position on the photo image at which the handwritten characters and pictures will be superposed and combined.
When the document sheet generated by the above-described method is read, it becomes necessary to distinguish the printed background image from the handwritten region and extract the handwritten characters and pictures. U.S. Patent Application Publication No. US 2005/0213174 discusses a technique for lightly printing the background image on the document sheet. When reading the document sheet, a threshold value is set as to the luminance, and the portion of the read image whose luminance value is lower than the threshold value is determined to be the portion handwritten by the user.
Moreover, Japanese Patent Application Laid-Open No. 2000-295565) discusses a method for combining the standard image with the photo image. A frame image recorded on a recording medium such as a memory card is read out and combined with the photo image. The photo image is then decorated and printed.
The above-described techniques can be used to combine the standard image with the photo image, and further with the image handwritten by the user. In such a case, the standard image and the lightly printed background image (hereinafter referred to as a reference image) are superposed on the handwritten region of the document sheet and printed. The user can thus write the characters or pictures while confirming the combined result. When such a document sheet is read, the printed standard image is distinguished from the reference image and extracted, similarly as the handwritten image. The standard image is then combined with the background image and printed.
However, when the standard image is printed in the handwritten region, read, and extracted from read image as described above, the extracted image may become affected by the background color of the document sheet. In particular, a white portion or a light color region in the extracted image may become affected by the background color and thus become different from the colors in the original standard image data. Since the extracted image is to be combined with the background image, the color tone of the standard image in the combined result may become different from the color tone of the standard image data. Further, color characteristics of a printing process and a reading process may further change the color tone of the standard image, so that the combined result may become unnatural.